This invention relates generally to mining roof bolts and, more particularly, to a roof bolt adapted to be anchored within a bore in the mine roof by resin adhesive material.
The existing roof bolts, such as shown, for example, in U.S Pat. No. 3,940,941, comprise a rod, usually formed of metal bar stock of the type used to reinforce concrete ("rebar"). Installation of the bolt in the roof of a mine includes the steps of: drilling a bore in the roof, inserting charges of unmixed resin therein, inserting the rod into the bore, mixing the resin by rotating the rod and, in a "fully grouted" system, continuing the application of pressing force until the resin has hardened thereby securing the rod to the roof. In "point anchored" and simultaneous "point anchored" and "fully grouted" bolting systems, such as shown, for example, in U.S. Pat. No. 4,303,354, only enough fast setting resin is provided in the bore to secure the bolt at its upper end and along the upper portion of its length to the surfaces of the roof defining the bore. The bolt may be three or more feet long, a relatively long lower portion of the length is then ungrouted (for "point anchored" bolt system) or filled with a slow setting resin (for simultaneous "point anchored" and "fully grouted" bolt system). Rotating the nut after the fast setting resin in the upper portion of the bore hardens with the nut pressing up against a roof bolt plate, but before the slow setting resin of the simultaneous "point anchored" and "fully grouted" system has hardened, tensions the lower portion of the bolt and effects a clamping or compressing of the roof strata between the hardened fast setting resin and the roof plate.
The existing roof anchoring bolts in the "fully grouted", "point anchored", and simultaneous "point anchored" and "fully grouted" bolting systems provide insufficient mixing of the resin upon rotation of the bolt to achieve the desired degree of homogenization of the resin. The incomplete mixing of the resin components upon hardening of the resin results in a lower than optimal bonding of the resin.
Among the several objects and features of the present invention may be noted the provision of a roof bolt for anchorage in a hole in the roof of a mine which is capable of quickly and thoroughly blending the resin adhesive; the provision of such a bolt which has increased load supporting capacity; the provision of such a roof bolt which can be formed by modifying commercially available resin bonded bolts; the provision of such a bolt which can be readily installed in the roof of the mine by standard roof bolting machines; and the provision of such a roof bolt which is of relatively simple and inexpensive construction.
Generally, the roof bolt of the present invention is adapted to be inserted into a hole drilled in a roof of an underground passage. The bolt is to be anchored in the hole by resin adhesive held in a bag inserted into the hole prior to the insertion of the roof bolt. The roof bolt punctures the bag upon insertion into the hole, and then the bolt is rotated about its longitudinal axis to facilitate setting the resin for anchoring the roof bolt in the hole. The roof bolt comprises a bar and a plurality of tabs on the bar at locations spaced longitudinally thereof. The tabs project radially outwardly from the bar for thoroughly blending the resin adhesive upon rotation of the bar thereby improving the bond of the resin adhesive to the bolt and for providing a support against loads directed generally outwardly of the hole.
Other objects and features will be in part apparent and in part pointed out hereinafter.